Valves are parts opening/closing the intake port and the exhaust port of the combustion chamber in an engine, in which an intake valve allows air for combustion to flow into the combustion chamber and an exhaust valve allows the gas burned by compression and explosion in the combustion chamber to be discharged outside.
The engine valves repeat high-speed operation, similar to the driving system such as a piston or a crankshaft, and the intake valve and the exhaust valve make one reciprocating motion for every two revolutions of the engine when the engine operates at 2000 rpm in a four-stroke internal combustion engine and make one hundred reciprocating motions per minutes, which causes a very severe operating condition.
Valves mainly make a vertical straight motion and also make a rotating motion about a vertical axis and a valve guide is the part that functions as a guide making the motions smooth.
Referring to FIG. 1, a valve guide 200 is usually formed in a cylindrical shape fixed to an engine block 10, has engine valves 100 therein to guide the vertical reciprocating motion of the engine valves 100, and is made of a relatively soft material in comparison to the engine valves 100 such that the valves are not worn out.
Wear is generated by friction due to a reciprocating motion between the engine valve 100 and the valve guide 200 and the amount of wear of the valve guide 200 is large, such that the gap between the engine valve 100 and the valve guide 200 increases, which may cause noise in the reciprocating motion of the engine valve and malfunction of the valve.
Further, a lubrication film is formed between the engine valve 100 and the valve guide 200 by injecting a lubricant in order to reduce the amount of wear of the valve guide 200, but it is preferable to keep the gap between the engine valve and the valve guide narrow within a range where the valve can reciprocate such that the lubricant does not flow into the engine combustion chamber 20 along the valve.
That is, when the amount of lubrication is too large, the lubricant oil flowing into the engine combustion chamber 20 increases, such that the amount of noxious exhaust gas due to combustion of the oil increases and the amount of consumed lubricant increases, whereas when the amount of lubrication is small, the friction between the valve and the valve guide increases.
Referring FIGS. 1 and 2, a circular stem seal 300 is fitted between the engine valve 100 and the valve guide 200 to stably guide the reciprocating motion of the engine valve 100 and to prevent the lubricant from excessively flowing to the engine valve 100.
The stem seal 300 is a seal fitting on one end of the valve guide 200 and surrounding the cylindrical main body portion of the engine valve 100, and generally has a ring shape.
The material of the stem seal 300 is usually an elastic material with predetermined elasticity such as rubber, surrounds the engine valve 100, and scrapes the lubricant off the surface of the engine valve 100 while guiding the reciprocating motion of the engine valve 100, such that it can prevent the lubricant from flowing into the engine combustion chamber.
The stem seal 300 is generally fixed to the upper end of the valve guide 200 by a stem seal case 330 and circumferentially surrounding the main column portion of the engine valve by a stem seal fixing spring 320 in close contact with the engine valve 100.
Further, the stem seal 300 has a contact portion called a stem seal rib 310 directly scraping the lubricant while guiding a reciprocating motion in close contact with the column portion of the engine valve 100 and is divided, in accordance with the number of formed stem seal ribs 310, into a single rib type with one rib, as illustrated in FIG. 2 (a), and a multi-rib type with two or more ribs, as shown in FIG. 2 (b).
The multi-rib type of stem seal is complicated in structure and expensive in comparison to the single rib type of stem seal, but a plurality of ribs, the contact portions, are formed, such that the function of removing a lubricant film and the pressing force for guiding the reciprocating motion of the valve are excellent.
When the gap between the engine valve and the valve guide increases, the lubricant film also increases, such that the amount of lubricant to be scraped increases, and it is necessary to use an expensive multi-rib type of stem seal in order to prevent the engine valve from slightly inclining in the valve guide.
As a result, since it is difficult for the valve to stably operate and it is necessary to use an expensive stem seal in order to remove an excessive lubricant, when the gap between the engine valve and the valve guide is increased by wear, it is required to keep effective lubrication conditions between the engine valve and the valve guide in order to reduce wear.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.